1. Field of the Invention
The present invention relates to an ultrasonic cleaner for irradiating an object to be cleaned in a cleaning liquid with ultrasonic waves generated from an ultrasonic transducer and to a wet treatment nozzle comprising the same.
2. Related Art
Heretofore, an ultrasonic shower cleaner 450 as shown in FIG. 21 has been used to clean liquid crystal panels and semiconductor wafers. In this ultrasonic shower cleaner 450, a hollow portion 452 for storing a cleaning liquid S is formed in the inside of a housing 451 and a liquid feed port 453 for supplying the cleaning liquid S into the hollow portion 452 is formed in an upper portion of a side wall of the housing 451 as shown in the figure. A nozzle 454 for discharging the cleaning liquid S is formed in the lower portion of the housing 451 and an ultrasonic transducer 455 is installed on the top surface of the housing 451. To clean an object P to be cleaned, this object P is caused to pass under the ultrasonic shower cleaner 450 and the cleaning liquid S is poured upon the surface of the object P by driving the ultrasonic transducer 455 by means of an unshown ultrasonic wave generator.
However, as the amount of the cleaning liquid is large in this cleaning method, a water-saving ultrasonic cleaner 460 shown in FIG. 22 is conceivable. This ultrasonic cleaner 460 has a housing 461 whose center portion 461a is depressed and whose end portion 461b is formed like a visor, an ultrasonic transducer 462 is placed on the surface of the center portion of the housing 461, and the object P passing through the cleaning liquid S under the housing 461 is irradiated with ultrasonic waves to be cleaned by vibrating the ultrasonic transducer 462.
An ultrasonic cleaner 470 shown in FIG. 23 is also conceivable though its cleaning method is similar to the above cleaning method. This ultrasonic cleaner 470 has a first housing 471 whose center portion 471a is depressed and whose end portion 471b around the center portion 471a is formed like a visor and a second housing 472 surrounding this first housing 471, whose center portion 472a is depressed and whose end portion 472b around the center portion 472a is formed like a visor. A packing 473 is sandwiched between the end portions 471b and 472b of these housings 471 and 472, and a hollow portion 474 is formed between the first housing 471 and the second housing 472. Further, a liquid for preventing empty heating, such as water 475, is filled in this hollow portion 474 and an ultrasonic transducer 476 is installed on the surface of the center portion of the first housing 471 so that the object P passing through the cleaning liquid S under the second housing 472 is irradiated with ultrasonic waves through water 475 in the hollow portion 474 to be cleaned by vibrating the ultrasonic transducer 476.
In the case of the ultrasonic cleaner 460 shown in FIG. 22 which is of a water-saving type, the vibration energy of the ultrasonic transducer 462 vibrates the bottom surface of the housing 461 and is radiated onto the object P through the cleaning liquid S. However, it also vibrates the wall surface of the housing 461, resulting in the waste of energy.
In the case of the ultrasonic cleaner 470 shown in FIG. 23, the thickness of the packing slightly differs according to clamping force, whereby the thickness of the hollow portion 474, that is, the depth of water filled in the hollow portion 474 differs. In this system that the object is irradiated with ultrasonic waves through water, sound pressure radiated from the sound wave radiation surface which is the bottom surface of the center portion of the second housing greatly changes according to variations in the depth of water from the relationship between the wavelength of an ultrasonic wave and the depth of water. In other words, the radiation sound pressure is greatly affected by the clamping force of the packing and lacks stability. When the depth of water is not appropriate and radiation sound pressure from the ultrasonic wave radiation surface is small, part of energy radiated from the ultrasonic transducer which is not used effectively may be used and wasted as energy for vibrating the wall surface of the second housing and may affect other devices by the vibration of the housing.